1. Field of the Invention
This invention relates to a noise control apparatus, and particularly to a noise control apparatus capable of more effectively accomplishing a sound volume reduction by use of a sound arresting wall and others.
2. Description of the Prior Art
It is well known that sound arresting walls and the like for reducing sound volumes have been developed as the interest in various noise nuisances has highly grown. Although it is said that a noise source countermeasure which to deal with the noise source is a matter calling for prior settlement in the field of overcoming the noise nuisances, the noise source countermeasure is limited and is difficult to apply in many cases. As a common sound arresting method, there has been adopted a method of isolating the propagation of sounds by the provision of an obstacle such as a sound arresting wall between a noise source and a sound receiving point, or a method of completely enclosing the noise source for isolation. However, it is natural that, in the former, the sound arresting wall is limited in sound arresting effect, and, the latter is disadvantageous in that, because of dealing with the other factors such as heat and exhaust gases, construction thereof becomes complex, and sometimes, it becomes impracticable.
For specific example, as a measure to counter a train noise nuisances generated by the travel of railroad vehicles such as a bullet train at present, sound arresting walls are principally adopted. Nevertheless, due to the fact that the noise is diffracted over the sound arresting walls, this measure is limited in sound volume reducing effect, and particularly, such a result has been proven that, in the district where the noise source is open to the eye, the effect by the sound arresting walls is hardly achieved. To overcome this disadvantage, it is conceivable to adopt a shelter system in which the total length of the railroad is completely enclosed as described above, which, however, is disadvantageous in that this system is almost impracticable in consideration of a so-called sunshin right, costs, ventilation and psychological reactions on the part of passengers.
The abovedescribed problems are similarly true of a measure to counter automobile travel noises on highways and mechanical noises generated in factories.